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Shimano 'light action' derailleur?
#1
Anybody know what a Shimano Light Action derailleur is, from the 80s?

80s model, Japan manufacture, Univega Nuovo Sport ser no. 0A39851

Has "Shimano Light Action" written on rear derailleur body. I believe it is the 'short body' type.

Has a Shimano front derailleur, just says Shimano on the cage and on the collar that mounts it to the seat tube. On the back side of the cage is stamped 'shimano FD'.

The crankset: Has "Signature" stamped on the outside of the crank arms, (matches the "Signature" stamped on the handlebar, I believe this is a Univega way of saying 'our quality'). On the back of the crank arm is stamped 165. The bolt or whatever that holds the crank together says "Univega cotterless".

The bottom bracket is toast so this justifies upgrading (only husband needs justification, not me LOL). Appears to have original chain and rear gears (not a cassette I don't think). It is 2 x 6, used to be 2 x 3 with biopace on the front chainrings. Glad that is gone. Small front gear is marked 42 on the back, that means 42 teeth right?

Did take some pictures but have to figure out how to get them posted.
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#2
(05-27-2013, 06:17 PM)redfoxglove Wrote:  Anybody know what a Shimano Light Action derailleur is, from the 80s?

80s model, Japan manufacture, Univega Nuovo Sport ser no. 0A39851

Has "Shimano Light Action" written on rear derailleur body. I believe it is the 'short body' type.

Has a Shimano front derailleur, just says Shimano on the cage and on the collar that mounts it to the seat tube. On the back side of the cage is stamped 'shimano FD'.

The crankset: Has "Signature" stamped on the outside of the crank arms, (matches the "Signature" stamped on the handlebar, I believe this is a Univega way of saying 'our quality'). On the back of the crank arm is stamped 165. The bolt or whatever that holds the crank together says "Univega cotterless".

The bottom bracket is toast so this justifies upgrading (only husband needs justification, not me LOL). Appears to have original chain and rear gears (not a cassette I don't think). It is 2 x 6, used to be 2 x 3 with biopace on the front chainrings. Glad that is gone. Small front gear is marked 42 on the back, that means 42 teeth right?

Did take some pictures but have to figure out how to get them posted.

Shimano's Light action shifting system is basically before Shimano did their SIS indexed Shifting system. It's basically a frictional shifting system with a micro ratcheting. I helped a friend fix up of their bike which was a 1986 Centurion Accordo which has Shimano's Light action system such as derailleurs and stem shifter which ratcheted.

Yes 42/T means 42 Teeth.

If it's the original chain, it's highly possible that the chain needs to be replaced especially if it's been ridden a lot. Check for chain stretch.

If it's stretched too far, you'll need to replace the chain plus freewheel cluster in the rear..

IF you replace the rear too, you can easily switch that out to a 7 speed vs 6 speed and just add a washer to the right side of rear wheel so the 7 speed freewheel can clear the frame.


That's the great thing about friction based shifters you can add more gears and you don't have to worry about the shifters. However, you'll need to adjust the limiters of the rear derailleur.

As for the bottom bracket... you can maybe replace it with a modern squared tapered Bottom bracket sealed cart... or find a cheap modern road crankset that includes bottom bracket.

Make sure when you take apart the bottom bracket find out what is written on the spindle say for example 3L or 3P

there's a list of stuff that's on Sheldon Brown's website regarding about older bottom bracket spindles equal to what size of modern spindle sizes.

But if you get a modern road crankset with bottom bracket that comes bundled with it, you don't have to worry about bottom bracket spindle length.

Note the 165mm is the Crankarm Length which is great for shorter riders so you spin more vs mashing.
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#3
Shimano's Light action shifting system is basically before Shimano did their SIS indexed Shifting system. It's basically a frictional shifting system with a micro ratcheting. I helped a friend fix up of their bike which was a 1986 Centurion Accordo which has Shimano's Light action system such as derailleurs and stem shifter which ratcheted.

Yes 42/T means 42 Teeth.

If it's the original chain, it's highly possible that the chain needs to be replaced especially if it's been ridden a lot. Check for chain stretch.

If it's stretched too far, you'll need to replace the chain plus freewheel cluster in the rear..

IF you replace the rear too, you can easily switch that out to a 7 speed vs 6 speed and just add a washer to the right side of rear wheel so the 7 speed freewheel can clear the frame.


That's the great thing about friction based shifters you can add more gears and you don't have to worry about the shifters. However, you'll need to adjust the limiters of the rear derailleur.

As for the bottom bracket... you can maybe replace it with a modern squared tapered Bottom bracket sealed cart... or find a cheap modern road crankset that includes bottom bracket.

Make sure when you take apart the bottom bracket find out what is written on the spindle say for example 3L or 3P

there's a list of stuff that's on Sheldon Brown's website regarding about older bottom bracket spindles equal to what size of modern spindle sizes.

But if you get a modern road crankset with bottom bracket that comes bundled with it, you don't have to worry about bottom bracket spindle length.

Note the 165mm is the Crankarm Length which is great for shorter riders so you spin more vs mashing.
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Haykong, thank you for this info. I will look at Sheldon's website for more detail on the bottom bracket. One (really young) bike guy at rei today told me it was highly unlikely I could get this bike to accommodate a 7 or 9 speed. The bike was 3 x 6 at one time, now it's 2 x 6. So you're suggesting it might accommodate a 7 gear cassette in the back.

We bought a chaingauge thingy at rei today so we can measure all our bikes for when they need new chains. The chain does not need to be changed according to this gauge, it is measuring less than 0.5 (the indicator tab does not fit into the chain space) of wear. Maybe a new chain has been put on the bike somewhere along the way, maybe when they took the biopace off the front.

So the chain is good, the back freewheel is still good (wear is noted but not over wear), I want a triple on the front not a double, and the bottom bracket is toast.

Glad to know that you have some experience with this light action thing. I note that it seems like it's indexed, but it's not. You explained why.

If I can get the rear derailleur dialed in to where it holds the low gears, I might be okay with just replacing the bottom bracket and leave this baby in mostly stock condition. But replacing the bottom bracket opens up a can of worms doesn't it? Isn't that why people junk bikes when the bottom bracket goes bad?
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